1. Field of the Invention
The present invention relates to a flat panel display. More particularly, the present invention relates to a flat panel display and method of manufacturing the same.
2. Description of the Related Art
Flat panel displays, e.g., an organic light emitting display (OLED) and a liquid crystal display (LCD), are thin and have low voltage operation, and have been replacing bulky, high voltage operation cathode ray tubes (CRTs) as display devices.
The OLED is a self-emitting display device in which electrons and holes injected into organic material through an anode and a cathode are recombined to generate excitons, and light with a certain wavelength is emitted by the generated excitons. Thus, the OLED, unlike an LCD, does not require a separate light source, e.g., a backlight, and, thus, consumes less power while realizing a wide viewing angle and a high response speed.
OLEDs may be divided into a passive matrix type and an active matrix type depending on a driving method thereof. Recently, active matrix type OLEDs have been employed, due to their low power consumption, high precision, high response speed, wide viewing angle and small thickness. In such an active matrix type OLED, a pixel region for light emitting or display is formed on a substrate, and a non-pixel region is formed on the substrate surrounding the pixel region.
Pixels serving as the basic unit for image representation may be arranged in a matrix on the pixel region. Light emitting elements may include a first electrode, e.g., an anode, a light emitting layer and a second electrode, e.g., a cathode, stacked in that order, and may be provided for each of the pixels. The light emitting layer may be made of an organic material for generating red (R), green (G) and blue (B) colors, respectively. A transistor, e.g., a thin film transistor (TFT), may be connected to the light emitting elements and may be arranged for each of the pixels to separately control the pixels. Pads may be formed on the non-pixel region and may be electrically connected to the pixels. The electric signals generated from an external driving circuit may be applied to the pixels through these pads.
The external driving circuit may be connected to the pads through, e.g., a flexible printed circuit (FPC), a chip on glass (COG) or a tape carrier package (TCP). The FPC and COG may be connected to the pads using an adhesive, e.g., an anisotropic conductive film (ACF).
In a method of manufacturing the active matrix type OLED, the TFT and the pad may be formed on the pixel region and the non-pixel region of the substrate, respectively. Then, a planarizing layer may be formed on the overall surface of the substrate so as to cover the TFT and the pad. The planarizing layer may then be patterned so as to expose a portion of the TFT and the pad, and a light emitting element may be formed on the planarizing layer in the pixel region so as to connect with the TFT.
The planarizing layer may be made of an organic material, e.g., acryl, and may be relatively thick in order to remove a step due to a height difference between the pixel region and the non pixel region. However, the thicker the planarizing layer becomes, the more a height difference between the pad of the non-pixel region and the planarizing layer increases. Therefore, conductive balls of the ACF may not be sufficiently compressed when connecting, e.g., the FPC and COG to the pads. Thus, contact failure may occur between the pads and the FPC and COG.